Underfilling material for semiconductor package

ABSTRACT

An underfilling material for a semiconductor package holding semiconductor elements on a carrier substrate mounted on a circuit board, containing a one-pack type thermosetting urethane composition which preferably comprises a urethane prepolymer having a terminal isocyanate group, which is obtained by reacting a polyol with an excessive amount of a polyisocyanate, and a fine powder-coated curing agent comprising a curing agent which is in a solid state at room temperature and surface active sites of which are covered with a fine powder. This composition can achieve both the low temperature curing properties and the storage stability.

This is a 371 of PCT/JP00/004490 filed Jul. 6, 2000, published inEnglish, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an underfilling material forsemiconductor packages. In particular, the present invention relates toan underfilling material which is used when a semiconductor packageholding semiconductor elements on a carrier substrate is mounted onto acircuit board, a mounted board produced by such mounting, and arepairing method of a mounted board.

PRIOR ART

The above-described type of the mounted board is used in applicationsrequiring high reliance such as automobile equipment, computers, and thelike, and also mobile phones which have been mass-produced with the widespread thereof. In general, such a mounted board is produced by mountinga semiconductor package holding semiconductor elements on a carriersubstrate to a circuit board, that is, by bonding the semiconductorpackage onto the circuit board with solder balls.

In the case of mobile phones, bond-failure of the solder ball may occurby the deformation of the substrate caused by falling shock, externalpressure generated with the operation of buttons, etc. Thus, areinforcing method is employed by filling an underfilling material inspaces around the solder-bonded parts and curing it to seal them. As theunderfilling material used to improve the reliability of the connectionby reinforcing, one-pack type or two-pack type thermosetting epoxy-basedmaterials containing epoxy resins, curing agents and plasticizers arewidely and mainly used (cf. JP-A-10-204259).

However, the epoxy-based materials should be thermally cured for 30minutes at 80° C. or 10 minutes at 150° C. When the low temperaturecuring properties are enhanced by the adjustment of compositions, theepoxy-based materials should be stored at a low temperature of about 5°C. or less. In addition, when the epoxy-based materials are used as theunderfilling materials, and the connection failures are found, the curedproducts, which are bonded to the circuit board, should be removed oneby one, by heat melting them and/or swelling them with solvents in therepairing works after detaching the semiconductor package from thecircuit board. Therefore, the conventional epoxy-based materials do nothave satisfactory repairing properties required at the work spot.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an underfillingmaterial for a semiconductor package, which can achieve both the lowtemperature curing properties and the storage stability, and solve theabove problems in repairing, that is, an underfilling material which canbe cured at a temperature of at least 60° C., for example, at 70° C. for20 minutes or at 80° C. for 10 minutes, and can be stored at roomtemperature.

Another object of the present invention is to provide a novel mountedboard comprising a semiconductor package holding semiconductor elementson a carrier substrate which is mounted on a circuit board.

A further object of the present invention is to provide a method foreasily repairing a mounted board.

According to the first aspect of the present invention, there isprovided a mounted board comprising a circuit board and a semiconductorpackage holding semiconductor elements on a carrier substrate, whereinsaid semiconductor package is connected to said circuit board withsolder balls, and spaces between solder connected parts are filled withan underfilling material which consists essentially of a one-pack typethermosetting urethane composition.

According to the second aspect of the present invention, there isprovide a method for producing a mounted board of the present invention,comprising the steps of:

connecting said semiconductor board to said circuit board with saidsolder balls,

then filling the spaces between solder connected parts with saidunderfilling material, and

curing said underfilling material to seal said mounted board.

According to the third aspect of the present invention, there isprovided a method for producing a mounted board of the present inventioncomprising the steps of:

applying the surface of said circuit board with said underfillingmaterial,

connecting said semiconductor board to said circuit board with saidsolder balls,

and curing said underfilling material to seal said mounted board.

According to the fourth aspect of the present invention, there isprovide an underfilling material for a semiconductor package holdingsemiconductor elements on a carrier substrate mounted on a circuitboard, consisting essentially of a one-pack type thermosetting urethanecomposition.

According to the fifth aspect of the present invention, there isprovided a method for repairing a mounted board of claim 1 comprisingthe steps of:

partly heating at least one of said semiconductor package and saidcircuit board to a temperature in the range between 180° C. and 350° C.,

melting said cured underfilling material and optionally said solder,

removing said semiconductor package from said circuit board and

mounting said semiconductor package or a new semiconductor package onsaid circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of the mounted board according tothe present invention.

FIG. 2 is a schematic cross section of the mounted board of FIG. 1 afterthe semiconductor package is detached from the circuit board in thecourse of repairing.

DETAILED DESCRIPTION OF THE INVENTION

A typical example of a one-pack type thermally curable urethanecomposition to be used according to the present invention is a urethanecomposition comprising a urethane prepolymer having a terminalisocyanate group which is prepared by the reaction of a polyol with anexcessive amount of polyisocyanate (hereinafter referred to as“NCO-containing prepolymer”), and a fine powder-coated curing agentcomprising a curing agent which is in a solid state at room temperatureand the surface active sites of which are covered with a fine powder.

This urethane composition may contain any conventional additives such asplasticizers (e.g. ester plasticizers based on phthalic acid, isophtalicacid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaricacid, trimellitic acid, pyromellitic acid, phosphoric acid, sulfonicacid, etc.); adhesive promoters, for example, silane coupling agents(e.g. mercaptosilane, epoxysilane, vinylsilane, etc.), titanate couplingagents, aluminum coupling agents, epoxy resins, phenol resins, etc.;stabilizers (e.g. hindered phenol type, monophenol type,bis-trispolyphenol type, thiobisphenol type stabilizers, etc.);dehydrants (e.g. calcium oxide, zeolite, silca gel, etc.); dyes andpigments; and the like.

The viscosity of such a thermally curable urethane composition isusually adjusted in the range between 500 and 50,000 mPa.s, preferablybetween 1,000 and 20,000 mPa.s.

The NCO-containing prepolymer may be prepared by reacting a polyol andan excessive amount of a polyisocyanate. Usually, an equivalent ratio ofNCO to OH is from 1.5:1 to 2.5:1, preferably from 1.9:1 to 2.2:1. TheNCO-containing prepolymer has a molecular weight of 800 to 50,000,preferably 1,000 to 10,000.

Examples of the above polyol include polyetherpolyols (e.g.polyoxyalkylene polyol (PPG), modified polyetherpolyol,polytetraethylene ether glycol, etc.), polyesterpolyols (e.g. condensedpolyesterpolyols, lactone-based polyesterpolyols, polycarbonatediols,etc.), polyols comprising backbones having C—C bonds (e.g. acrylpolyols,polybutadiene polyols, polyolefine polyols, caster oil, etc.), and thelike.

Examples of the above polyisocyanate include tolylene diisocyanate(TDI), 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate,hexamethylene disocyanate, isophorone diisocyanate, lysin diisocyanate,isopropylidenebis(4-cyclohexylisocyanate), hydrogenated xylylenediisocyanate, etc.

The NCO-containing prepolymer prepared using a polyetherpolyol as apolyol (PPG type prepolymer) or, in particular, a hydrocarbon polyol asa polyol (PH type prepolymer) is advantageous, since it can impartelectrical insulation to the material, but it may increase the viscosityof the material. Thus, the HC or PB type prepolymer is preferably usedin combination with the NCO-containing prepolymer comprising PPG (PPGtype prepolymer). In this case, a weight ratio of the HC or PB typeprepolymer to the PPG type prepolymer is usually from 9:1 to 2:8,preferably from 9:1 to 5:5. Furthermore, a NCO-containing prepolymer,which is prepared by reacting a mixture of the PB type polyol and PPG ina specific ration with an excessive amount of a polyisocyanate, may beused.

The fine powder coated curing agent may be prepared with ashear-friction mixing system by grinding the curing agent which is inthe solid state at room temperature to a median particle size of 20 μmor less while adding thereto the fine powder in a weight ratio of thecuring agent to the fine powder in the range between 1:0.001 to 1:0.7,preferably between 1:0.01 to 1:0.5, and mixing and grinding them so thatthe median particle size of the fine powder becomes 2 μm or less,whereby the fine powder is adhered to the surface of the particles ofthe solid curing agent.

Alternatively, the fine powder-coated curing agent may be prepared bymixing the finely preground solid curing agent and the fine powder witha high speed impact type mixer (e.g. jet mill) or a compression sheartype mixer. The use of the high speed impact type mixer is preferable.

Examples of the curing agent which is in the solid state at roomtemperature include imidazole compounds (e.g. imidazole,2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole,2-isopropylimidazole, 2-phenyl-imidazole, 2-dodecylimidazole,2-undecylimidazole, 2-heptadecyl imidazole, their salts with carboxylicacids such as acetic acid, lactic acid, slicylic acid, benzoic acid,adipic acid, phthalic acid, citric acid, tartaric acid, maleic acid,trimellitic acid, etc.); imidazoline compounds (e.g.2-methylimidazoline, 2-phenylimidazoline, 2-undecylimidazoline,2-heptadecylimidazoline,1-(2-hydroxy-3-phenoxypropyl)-2-phenylimidazoline,1-(2-hydroxy-3-butoxypropyl)-2-methylimidazoline, etc.); aromatic aminecompounds (e.g. 4,4′-, 2,4′-, 3,3′- or 3,4′-diaminodiphenylmethane,2,2′- 2,4′- or 3,3′-diaminobiphenyl, 2,4- or 2,5-diaminophenol, o- orm-phenylenediamine, 2,3-, 2,4-2,5-, 2,6- or 3,4-tolylenediamine, etc.);aliphatic amine compounds (e.g. 1,8-octanediamine, 1,10-decanediamine,1,12-dodecanediamine, 1,14-tetradecanediamine, 1,16-hexadecanediamine,etc.); guanidine compounds (e.g. dicyanediamine, etc.); acid anhydrides(e.g. phthalic anhydride, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, methylated hexahydrophthalic anhydride,trimellitic anhydride, etc.); dibasic carboxylic acid dihydrazide (e.g.acipic acid dihydrazide, sebacic acid dihydrazide, etc.); guanamines(e.g. benzoguanamine, etc.); melamine; amine adducts (e.g. adducts of2-ethyl-4-methylimidazole and bisphenol A epoxy resins, etc.); and thelike.

Examples of the fine powder include inorganic powders (e.g. titaniumoxide, calcium carbonate, clay, silica, zirconia, carbon, alumina, talc,etc.); and organic powder (e.g. polyvinyl chloride, acrylic resins,polystyrene, polyethylene, etc.); and the like.

When the solid curing agent and the fine powder are mixed and ground,static electricity may be generated and thus the fine powder may beadhered to the surfaces of the particles of the solid curing agent, orthe particles of the solid curing agent may be partially molten with aheat due to friction, impact or compression shear generated with themixer and thus the fine powder is adhered to the surfaces of theparticles of the solid curing agent, or the fine powder may bephysically anchored in the surfaces of the particles of the solid curingagent, or the surfaces of the particles of the solid curing agent may bechemically activated and thus the fine powder may be adhered to thesurfaces of the particles of the solid curing agent. Accordingly, theactive groups such as —NH₂ or —NH groups on the surfaces of theparticles of the solid curing agent can be coated with the fine powder.

The fine powder-coated curing agent can be activated by heating at atemperature equal to or higher than the melting point of the solidcuring agent, and therefore, the active groups, which are reactivated byheating, contribute to the curing reaction with the NCO groups of theNCO-containing prepolymer.

The amount of the fine powder-coated curing agent may be selected sothat the curing agent is present in substantially an equivalent amountto the NCO-containing prepolymer.

Another example of the one-pack type thermally curable urethanecomposition includes a polyisocyanate the NCO group of which isinactivated with a blocking agent (e.g. phenol type, oxime type orlactam type blocking agents), or a combination of an inactivatedpolyisocyanate, which is in the solid state at room temperature, with acuring agent (e.g. polyols, polyamines, etc.). The polyisocyanate may bethat used in the above preparation of the NCO-containing prepolymer.

Furthermore, a combination of a polyisocyanate with a inactivatedpolyamine curing agent.

Preferably, the one-pack type thermally curable urethane composition ofthe present invention may further contain an epoxy resin, anorganosilicone and/or a dehydrant.

The epoxy resin increases the physical properties of the cured productof the urethane composition of the present invention.

The amount of the epoxy resin may be from 5 to 30 wt. %, preferably from7 to 20 wt. %, based on the weight of the urethane composition.

When the amount of the epoxy resin is less than 5 wt. %, the physicalproperties of the urethane composition of the present invention may notbe improved. When the amount of the epoxy resin exceeds 30 wt. %, theviscosity of the urethane composition of the present invention tends toincrease so that the workability and penetrability deteriorate.

The epoxy resin may be any conventionally used epoxy resin. Specificexamples of the epoxy resin include the following ones:

(1) Glycidylamine epoxy resins

Epoxy resins having at least one N,N-diglycidylamino group, such asN,N,N′,N′-tetraglycidylaminodiphenylmethane, N,N-diglycidyl-m- orp-aminophenol glycidyl ether and their condensates. They arecommercially sold under ARALDITE® MY 720 (available from Ciba-Geigy),and EPOTOTE® 434 and YH 120 (both available from TOTO KASEIKABUSHIKIKAISHA).

(2) Novolak epoxy resins

Phenolic novolak epoxy resins such as EPIKOTE152 and 152 (both availablefrom Shell Chemical), DOW EPOXY RESIN DEN 431, 438, 439 and 485 (allavailable from Dow Chemical), RE-3055 (available from NIPPON KAYAKU),etc. Cresol novolak epoxy resins such as ECN 1235, 1273, 1280 and 1299(all available from Ciba-Geigy), EOCN 100, 102, 103 and 104 andEOCN-1020, 1025, 1027 3300 and 4400 (all available from NIPPON KAYAKU),QUATREX 3310, 3410 and 3710 (all available from Dow Chemical), etc.

(3) Bisphenol A epoxy resins

Bisphenol A epoxy resins such as EPIKOTE® 828, 834, 827, 1001, 1002,1004, 1007 and 1009 (all available from YUKA SHELL), DOW EPOXY DER 331,332, 662, 663U and 662U (all available from Dow Chemical), ARALDITE®6071, 7071 and 7072 (all available from Ciba-Geigy), EPICRONE 840, 850,855, 860, 1050, 3050, 4050 and 7050 (all available from DAINIPPON INKAND CHEMICALS), RE-310S and RE-410S (both available from NIPPON KAYAKU),etc. Urethane-modified bisphenol A epoxy resins such as ADEKA RESINEPV-6, EPV-9 and EPV-15 (all available from ASAHI DENKA KOGYO), etc.Brominated bisphenol A epoxy resins such as ARALDITE® 8011 (availablefrom Ciba-Geigy), DOW EPOXY RESIN DER 511 (available from Dow Chemical),etc.

(4) Alicyclic epoxy resins

ARALDITE® CY-179, CY-178, CY-182 and CY-183 (all available fromCiba-Geigy).

(5) Other epoxy resins

Bisphenol F epoxy resins such as EPIKOTE® 807 (available from YUKASHELL), RE-304S, RE-403S and RE-404S (all available from NIPPON KAYAKU),S-129 and 830S (both available from DAINIPON INK AND CHEMICALS).Resorcinol epoxy resins, tetrahydroxyphenylethane epoxy resins,polyalcohol epoxy resins, polyglycol epoxy resins, glyceroltrietherepoxy resins, polyolefin epoxy resins, epoxidized soybean oil, esterepoxy resins, phenolic epoxy resins, naphthalene epoxy resins,flame-retarded epoxy resins, and the like.

Among the above epoxy resins, the epoxy resins which are in the liquidstate at room temperature, can be used as such, while those which are inthe solid state at room temperature may be heated to their meltingpoints and molten, or solved by the co-use of the liquid epoxy resins.

The organosilicone compound can improve the adhesion properties andwettability. The organosilicone compound may be at least one compoundselected from the group consisting of silane coupling agents,organopolysilicones having terminal silanol groups, polyether-modifiedsilicones and modified organosilicones.

The amount of the organosilicone compound is usually from 0.01 to 5.0wt. %, preferably from 0.05 to 5.0 wt. %, based on the weight of theurethane composition.

When the amount of the organosilicone compound is less than 0.01 wt. %,the adhesion properties and penetrability of the urethane composition ofthe present invention may not be improved. When the amount of theorganosilicone compound exceeds 5 wt. %, the storage stability of theurethane composition of the present invention tends to deteriorate.

Examples of the silane coupling agent include aminosilane compounds(e.g. γ-aminopropyltriethoxysilane, β-aminoethyl-trimethoxysilane,γ-aminopropyldiethoxysilane, γ-allylaminopropyltrimethoxysilane,β-(β-aminoethylthioethyl)-diethoxymethylsilane,β-(β-aminoethylthioethyl) triethoxysilane,β-phenylaminopropyltrimethoxysilane,γ-cyclohexylaminopropyl-trimethoxysilane,γ-benzylaminopropyltrimethoxysilane,γ-(vinylbenzylaminopropyl)triethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyl-methyldimethoxysilane,β-(β-aminoethylaminomethylmethoxysilane,γ-[β-(β-aminoethylaminoethylamino)propyl]triethoxysilane,N-(3-triethoxysilylpropyl)urea, etc.), mercaptosilane compounds (e.g.3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane,mercaptomethyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, etc.),epoxysilane compounds (e.g.β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,[2-(3,4-epoxy-4-methylcyclohexyl)propyl]methyldiethoxysilane,(3-glycidoxypropyl)methyldiethoxysilane,3-glycidoxypropyl-trimethoxysilane, etc.), isocyanate silane compounds(e.g. γ-isocyanatepropyltriethoxysilane,γ-isocyanatepropyl-trimethoxysilane, etc.), and the like.

Examples of the silanol organopolysilicones having the terminal silanolgroups include polysiloxanes of the formulas:

wherein R₁ is a methyl group or a phenyl group, R₂ is a phenyl group, Phis a para-phenylene group, r is a number of 9 to 500, and s is 0 or anumber of 6% or less of r. They may be used singly or in admixture oftwo or more.

Specific examples of the commercially available organopolysiliconeshaving the terminal silanol groups are polydimethylsiloxane havingterminal silanol groups, diphenylsiloxane having terminal silanolgroups, polydimethyldiphenylsiloxane having terminal silanol groups,polytetramethyl-p-silylphenylenesiloxane, etc.

One example of the polyether-modified silicone is a compound of theformula:

wherein X₁ is —OH, —NH₂ or —NHR in which R is a linear or branched alkylgroup having 1 to 8 carbon atoms or a phenyl group; R₁₀ and R₁₁ are thesame or different and each a hydrogen atom, a methyl group or a phenylgroup; R₁₂ is a hydrogen atom or a methyl group; m is a number of 3 to300; n is a number of 1 to 100; and n′ is a number of 1 to 100.

One example of the modified organosilicone is an organosilicone preparedby reacting (a) a silicone compound having active hydrogen atoms at bothends, (b) a polyhydric active hydrogen compound, (c) a diisocyanatecompound and (d) a chain extender having active hydrogen atoms at bothends according to one of the following methods:

(i) First method:

Firstly the silicone compound having the active hydrogen atoms at bothends (a) is reacted with the diisocyanate compound (c) at a temperatureof 20 to 120° C. for 10 minutes to 120 hours, optionally in the presenceof a solvent to form a mono-adduct.

Examples of the solvent include ethyl acetate, butyl acetate, toluene,xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone,tetrahydrofuran, etc.

Separately, the polyhydric active hydrogen compound (b) and thediisocyanate compound (c) are reacted under the same conditions as thosein the above reaction to form another mono-adduct.

Then, the both mono-adducts are block addition reacted in the presenceof the chain extender having the active hydrogen atoms at both ends (d)at a temperature of 20 to 120° C. for 1 to 120 hours to obtain aurethane-modified silicone resin.

(ii) Second method:

The above four components (a) to (d) are block addition reacted in aone-batch system optionally in the presence of the above solvent toobtain a urethane-modified silicone resin.

One example of the silicon compound having the active hydrogen at theboth ends (a) is a compound of the formula:

wherein X₂ is —OH, —NH₂ or —NHR in which R is the same as defined above;R₁₃ and R₁₄ are the same or different and each a hydrogen atom, a methylgroup or a phenyl group, R₁₅ is an alkylene or alkylene ether grouphaving 1 to 12 carbon atoms; and p is a number of 3 to 300.

The silicone compound (V) has a molecular weight of 900 to 20,000,preferably 1,800 to 10,000.

Such silicone compounds are commercially sold under the trade names KF6001, KF6002 and KF 6003 (all available from Shin-Etsu Silicone),FM3311, FM3321 and FM4421 (all available from CHISSO), etc.

Examples of the polyhydric active hydrogen compound (b) include

wherein X₃ is —OH, —NH₂ or —NHR in which R is the same as defined above;R₁₆ is a hydrogen atom or a methyl group; R₁₇ is an alkylene grouphaving 1 to 12 carbon atoms or a group of the formula:

wherein R₁₈ and R₁₉ are the same or different and each a hydrogen atomor a methyl group, and Ph′ is an o-, m- or p-phenylene group which maybe hydrogenated; q is a number of 1 to 100; and q′ is a number of 1 to100 (e.g. polypropylene glycol, polyethylene glycol,polypropyleneethylene glycol, propylene and/or ethylene adducts ofbisphenol A), or a polyesterpolyol with hydroxyl groups at both endscomprising repeating units of the formula:

—R₂₀—CO—O—R₂₁—

wherein R₂₀ is a residue of an aliphatic or aromatic dicarboxylic acid;and R₂₁ is a residue of an aliphatic or aromatic dihydric alcohol,provided that R₂₀ and/or R₂₁ may be the same in all the repeating unitsor different from the repeating units to the repeating units to providea copolymer.

The molecular weight of the polyhydric active hydrogen compound (b) maybe from 500 to 10,000, preferably from 1,000 to 3,000.

Examples of the diisocyanate compound (c) include aromatic diisocyanates(e.g. 2,4- or 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), xylylene diisocyanate, etc.), and aliphaticdiisocyanates (e.g. hexamethylene diisocyanate, lysin diisocyanate,isophorone diisocyanate, hydrogenated MDI, hydrogenated TDI, etc.).

Examples of the chain extender having the active hydrogen atoms at theboth ends (d) include etylene glycol, propylene glycol, butanediol,dimethylolcyclohexane, methyliminodiethanol, dimethylolpropionic acid,ethylenediamine, hexamethylenediamin, etc.

When a silicone compound having active hydrogen atoms at both ends ofthe formula:

wherein R₁₃, R₁₄, R₁₅ and p are the same as defined above is used as thecomponent (a), a bisphenol A-propylene oxide adduct of the formula:

wherein q and q′ are the same as defined above and Ph is apara-phenylene group is used as the component (b), TDI is used as thecomponent (c), and butanediol is used as the component (d), the modifiedorganosilicone has a chemical structure of the formula:

wherein R₁₃, R₁₄, R₁₅, p, q, q′ and Ph are the same as defined above,and x is a number 1 to 10 and y is a number of 1 to 20.

A dehydrant can improve the storage stability of the urethanecomposition of the present invention. The amount of the dehydrant is 1to 10 wt. %, preferably 2 to 5 wt. %, based on the weight of theurethane composition.

Examples of the dehydrant include calcium oxide, zeolite, silica gel,ethyl silicate, ethyl orthophosphate, ethyl formate, methylorthoacetate, etc.

The one-pack type thermally curable urethane composition of the presentinvention may contain any conventional additives, if desired. Examplesof the additives include extenders, reinforcing agents, fillers (e.g.coal tar, glass fiber, boron fiber, carbon fiber, cellulose,polyethylene powder, polypropylene powder, quartz powder, mineralsilicates, mica, slate powder, kaolin, aluminum oxide trihydrate,aluminum hydroxide, chalk powder, gypsum, calcium carbonate, antimonytrioxide, bentonite, silica, aerosil, lithopone, barite, titaniumdioxide, carbonblack, graphite, ironoxide, goldpowder, aluminum powder,iron powder, etc.), pigments, organic solvents (e.g. toluene, xylene,methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butylacetate, etc.), reactive diluents (e.g. butyl glycidyl ether,N,N′-diglycidyl-o-toluidine, pheny glycidyl ether, styrene oxide,ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,1,6-hexanediol diglycicyl ether, etc.), non-reactive diluents (e.g.dioctylphthalate, dibutylphthalate, dioctyl adipate, petroleum solvents,etc.), modified epoxy resins (e.g. urethane-modified epoxy resins,alkyd-modified epoxy resins, etc.), and the like.

The mounted board according to the present invention may be produced byany conventional methods which are employed to produce the conventionalmounted boards, except that the one-pack type thermosetting urethanecomposition of the present invention is used as the underfillingmaterial for the semiconduct package.

Now, one preferred embodiment of the method for the production of themounted board according to the present invention will be explained bymaking reference to FIG. 1.

As shown in FIG. 1, the mounted board 1 is produced by connecting thesemiconductor package 2 to the circuit board 3 with solder balls 4 eachhaving a diameter of 300 to 800 μm at a ball pitch of 100 to 500 μm,filling the spaces between the solder balls 4 with the underfillingmaterial 5, that is, the one-pack type thermosetting urethanecomposition of the present invention, using a preciselymetering/discharging apparatus for liquids, and then heating the mountedboard at a temperature of 80 to 100° C. for 5 to 10 minutes to cure theurethane composition and seal the spaces.

The circuit board may be made of a resin such as a glass-reinforcedepoxy resin, an ABS resin, a phenol resin, etc.

The semiconductor package may be produced holding semiconductor elements(e.g. LSI, etc.) on a carrier substrate, that is, electricallyconnecting the semiconductor elements and the carrier substrate with ahigh-melting solder, an anisotropic conductive adhesive or a wire, andsealing them with a suitable resin to increase the reliability anddurability of the connections. The carrier substrate may be a substrateor a tape made of a ceramic such as Al₂O₃, SiN₃, Al₂O₃/SiO₂, or aheat-resistant resin such as a polyimide resin, or the resin used toproduce the above circuit board.

Examples of the semiconductor package are chip size packages (CSP), ballgrip arrays (BGA), and so on.

If poor connection is found in the mounted board, it can be repaired bythe following procedures:

i) First, as shown in FIG. 1, a part of the upper surface of thesemiconductor package 2 is heated with hot air A to a temperature of 180to 300° C. to melt the solder balls 4 in the soldered area, and thesemiconductor package 2 is detached (see FIG. 2).

ii) Then, one end of the composite 6 of the remaining underfillingmaterial 5′ and the remaining solder balls 4′ is pinched with a forcepsor any other tool (not shown), and the composite 6 is easily peeled offfrom the circuit board 3, while a hot air is blown on the lower surfaceof the circuit board 3 to heat it to a temperature of 180 to 350° C.,preferably 200 to 300° C.

After cleaning the surface of the circuit board 3, the semiconductorpackage is again mounted by the above procedures.

EXAMPLES

The present invention will be illustrated in detail by the followingExamples.

Examples 1-4

(1) Synthesis of a NCO-containing prepolymer

A polybutadiene based polyol and TDI were reacted with the NCO/OH ratiobeing 2.0 to obtain a NCO-containing prepolymer having a molecularweight of 1,500 (PH-based prepolymer).

(2) Fine powder-coated curing agent

1,10-Decanediamine (melting point: 60° C.) and titanium oxide having amedian particle size of 0.27 μm were mixed in a weight ratio of 1:0.3,and ground with a jet mill to obtain a fine powder-coated curing agenthaving a median particle size of 10 μm.

(3) Preparation of a one-pack type thermosetting urethane composition

i) Firstly, a NCO-containing prepolymer prepared from PPG and TDI(SUNPRENE SEL No. 3 available from SANYO KASEI; NCO content of 3.6 %;molecular weight of 7,000) (hereinafter referred to as “PPG-basedprepolymer”) and the NCO-containing prepolymer prepared in the above (1)(PH-based prepolymer) were mixed in a weight ratio shown in Table 1, andcured at 80° C. for 10 minutes. Then, the physical properties (with theJIS No. 3 dumbbell shaped sample) and electrical properties of the curedproduct were measured. The results are shown in Table 1.

TABLE 1 Run No. 1 2 3 4 5 6 7 Weight ratio of 100/0 90/10 70/30 50/5030/70 10/90 0/100 PPG-based prepolymer to PH-based prepolymer Physicalproperty 50% modulus 16.5 20.0 19.3 25.5 48.7 59.5 52.9 (kg/cm²)strength at break 38.7 40.3 43.9 53.4 90.9 78.5 57.5 (%) Maximumelongation 400 350 200 200 200 125 100 (%) Electrical propertyDielectric — — 4.97 4.61 4.23 3.7 3 constant (ε) Dielectric — — 0.05750.0428 0.04 0.0188 0.015 dissipation factor (tan δ) Volume resistivity1.0 × 10⁸> 1.0 × 10⁸> 2.70 × 10¹⁰ 8.70 × 10¹⁰ 1.29 × 10¹² 2.95 × 10¹³6.61 × 10¹⁶ (Ω · cm)

ii) Next, the mixed prepolymer No. 7 prepared in the above step i)(weight ratio of PPG-based prepolymer to PH-based prepolymer=30/70), thefine powder-coated curing agent prepared in (2), a plasticizer, abisphenol A epoxy resin, a silane coupling agent, polydimethylsiloxane,a stabilizer and a dehydrant were homogeneously mixed in amounts (wt.parts) of Table 2 to obtain a one-pack type thermosetting urethanecomposition having a viscosity shown in Table 2 (at 23° C.).

(4) Performance tests

The prepared composition was subjected to the following tests:

(a) Low temperature curing properties

A heating condition required for curing was measured when thecomposition was applied in a thickness of 2 mm on a steel plate. Thesteel plate was heated in an oven heated with hot air.

(b) Adhesion strength

Tensile shear adhesion strength was measured according to JIS K 6850using a glass-reinforced epoxy resin as a test piece.

(c) Penetrating properties

A time was measured, in which the urethane composition advanced in a gapof 500 μm between a pair of glass plates for a distance of 10 mm at 40°C. by the capillary action.

(d) Volume resistivity (Ω·cm)

According to JIS K 6911, a volume resistivity of the urethanecomposition was measured after keeping the composition at 23° C. for 1minutes while applying a voltage of 100 V.

(e) Repairing properties

A urethane composition was applied at a thickness of 500 μm on aglass-reinforced epoxy resin plate and cured at 80° C. for 20 minutes.Then, the coated plate was placed on a hot plate, and the coatedurethane composition was peeled off at a hot plate surface temperatureof 210° C., 220° C. and 230° C. The repairing properties were evaluatedby the peeling condition of the coated urethane composition, and rankedaccording to the following criteria:

A: Completely removed in the peeled state

B: Almost all the cured urethane composition removed

C: Splits remain on the circuit board

D: Repairing impossible

(f) Storage stability

The urethane composition was stored at 40° C. for 2 months and theviscosity of the composition was measured. Then, the increase (%) of theviscosity in comparison with the viscosity before storage wascalculated.

In Comparative Example 1, the urethane composition was stored only oneday, and then the viscosity was measured.

The results are shown in Table 2.

Comparative Example 1

The one-pack type thermosetting epoxy material (PENGUIN CEMENT 1090available from SUNSTAR GIKEN) was used and subjected to the sameperformance tests as in Examples 1 to 4.

The results are shown in Table 2.

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 C. Ex. 1 Mixed prepolymer 50 50 40 40Curing agent 13.5 13.5 15 15 Plasticizer¹⁾ 30 30 25 25 Epoxy resin²⁾ 2020 Silane 2.5 Coupling agent³⁾ Polydimethyl- 2.5 2.5 2.5 Siloxane⁴⁾Stabilizer⁵⁾ 0.1 0.1 0.1 0.1 Dehydrant 3 Viscosity (mPa · s) 8000 66005200 4900 5600 Low temperature 80° C. × 80° C. × 80° C. × 80° C. × 130°C. × Curing properties 10 min. 10 min. 10 min. 10 min. 10 min. Adhesionstrength 5.0 6.0 8.5 8.5 15.2 (N/mm²) Penetrating 50 45 40 40 40Properties (sec.) Volume resistivity 1.5 × 4.5 × 5.0 × 5.5 × 1.0 × (Ω ·cm) 10¹² 10¹³ 10¹³ 10¹³ 10¹⁶ Repairing Properties 180° C. C C C C D 220°C. B B B B D 230° C. A A A A D Storage stability 49 45 Not 25 50(viscosity measur- increase: %) able Notes: ¹⁾Tri(2-ethylhexyl)trimellitate + di(2-ethylhexyl) adipate in a weight ratio of 2:1.²⁾Bisphenol A epoxy resin (EPIKOTE ®828 available from YUKA SHELL).³⁾3-Glycidoxypropyltrimethoxy silane (KBM-351A (trade name) availablefrom Shin-Etsu Chemical). ⁴⁾Polyether-modified silicone (KF-351A (tradename) available from Shin-Etsu Chemical).⁵⁾Tetrakis[methylene-3-(3′,5′-di-tert.-butyl-4′-hydoxy-phenyl)propionate]methane(ADEKA STUB AO-60 available from ASAHI DENKA KOGYO).

As can be seen from the results of Table 2, the urethane compositions ofthe present invention have better low temperature curing properties andstorage stability than the conventional urethane material.

What is claimed is:
 1. A mounted board comprising a circuit board and asemiconductor package holding semiconductor elements on a carriersubstrate, wherein said semiconductor package is connected to saidcircuit board with solder balls, and spaces between solder connectedparts are filled with an underfilling material which consistsessentially of a on-pack type thermosetting urethane compositioncomprising: a urethane prepolymer having a terminal isocyanate group,which is obtained by reacting a polyol with an excessive amount of apolyisocyanate, wherein said urethane prepolymer is a mixture of aurethane prepolymer having a terminal isocyanate group comprising ahydrocarbon polyol as a polyol and a urethane prepolymer having aterminal isocyanate group comprising a polyoxyalkylene polyol in aweight ratio of 9:1 to 2:8, and a fine powder-coated curing agentcomprising a curing agent which is in a solid state at room temperatureand surface active sites of which are covered with a fine powder.
 2. Themounted board according to claim 1, wherein said curing agent which isin a solid state at room temperature is at least one curing agentselected from the group consisting of imidazole compounds, imidazolinecompounds, amine compounds, guanidine compounds, acid anhydrides,dibasic carboxylic acid dihydrazide, guanamines, melamine and amineadducts.
 3. The mounted board according to claim 1, wherein said finepowder is one material selected from the group consisting of titaniumoxide, calcium carbonate, clay, silica, zirconia, carbon, alumina, talc,polyvinyl chloride, acrylic resins, polystyrene and polyethylene.
 4. Themounted board according to claim 1, wherein said one-pack typethermosetting urethane composition further comprises at least oneadditive selected from the group consisting of epoxy resins,organosilicone compounds and dehydrants.